1. Field of the Invention
The present invention relates to an optical fiber applicable to a transmission line in optical communications, and an optical transmission system including this optical fiber.
2. Related Background Art
Conventionally, as a transmission line in optical communications, standard single-mode optical fibers having a zero-dispersion wavelength in a 1.3-.mu.m wavelength band (1280 nm to 1320 nm) have mainly been utilized. The transmission loss resulting from the main material (silica) of such an optical fiber has been known to become the lowest in a 1.55-.mu.m wavelength band (1530 nm to 1565 nm). In addition, optical fiber amplifiers using an Er-doped optical fiber can amplify light in the 1.55-.mu.m wavelength band at a high efficiency. For such a reason, dispersion-shifted optical fibers designed so as to have a zero-dispersion wavelength in the 1.55-.mu.m wavelength band are applied to transmission lines in wavelength division multiplexing (WDM) communications for transmitting a plurality of wavelengths of signal light. As for a light source for sending out signal light, device technologies for enabling light in the 1.3-.mu.m wavelength band and light in the 1.55-.mu.m wavelength band to be outputted have conventionally been established.